Method and apparatus for impedance matching in a power delivery system for remote plasma generation

Abstract

A plasma-generation system is provided that includes a variable-frequency microwave generator configured to generate microwave power and a plasma applicator configured to use the microwave power from the microwave generator to (i) ignite a process gas therein for initiating a plasma in a plasma ignition process and (ii) maintain the plasma in a steady state process. The system also includes a coarse tuner connected between the microwave generator and the plasma applicator. At least one physical parameter of the coarse tuner is adapted to be set to achieve coarse impedance matching between the microwave generator and the plasma generated during both the plasma ignition process and the steady state process. A load impedance of the plasma generated during the plasma ignition process and the steady state process is adapted to vary. The microwave generator is configured to tune an operating frequency at the set physical parameter of the coarse tuner.

What is claimed is: 
     
       1. A plasma-generating system comprising:
 a variable-frequency microwave generator configured to generate microwave power; 
 a plasma applicator configured to use the microwave power from the microwave generator to (i) ignite a process gas therein for initiating a plasma in a plasma ignition process and (ii) maintain the plasma in a steady state process, wherein a load impedance of the plasma generated during the plasma ignition process and the steady state process is adapted to vary over an impedance range; and 
 a coarse tuner connected between the microwave generator and the plasma applicator, wherein at least one physical parameter of the coarse tuner is adapted to be set to achieve coarse impedance matching between the microwave generator and the plasma generated during both the plasma ignition process and the steady state process; 
 wherein the microwave generator is configured to tune an operating frequency at the at least one set physical parameter of the coarse tuner, without altering the at least one set physical parameter of the coarse tuner during both the plasma ignition process and the steady state process, to achieve (i) ignition of the process gas during the plasma ignition process and (ii) optimization of the microwave power delivered to the plasma in the steady state process. 
 
     
     
       2. The plasma-generating system of  claim 1 , wherein the at least one physical parameter of the coarse tuner is set prior to both the plasma ignition process and the stead state process and remains unaltered during both the plasma ignition process and the steady state process. 
     
     
       3. The plasma-generating system of  claim 2 , wherein a value to set the at least one physical parameter of the coarse tuner ensures that the microwave power absorbed by the plasma over the impedance range of the plasma is within an operating frequency bandwidth of the microwave generator. 
     
     
       4. The plasma-generating system of  claim 3 , wherein the value is determined offline by at least one of microwave modeling or experimentation. 
     
     
       5. The plasma-generating system of  claim 1 , wherein the coarse tuner is a fixed stub tuner that includes at least a stub and a coupling antenna. 
     
     
       6. The plasma-generating system of  claim 5 , wherein the at least one physical parameter of the fixed stub tuner that remains unaltered during both the plasma ignition process and the steady state process comprises at least one of (i) a distance between the stub and a longitudinal axis of a dielectric plasma tube of the plasma applicator or (ii) a length of the stub. 
     
     
       7. The plasma-generating system of  claim 6 , wherein the stub length is set to about 1.21 inches prior to both the plasma ignition process and the stead state process. 
     
     
       8. The plasma-generating system of  claim 6 , wherein the distance is set to about 2.96 inches prior to both the plasma ignition process and the stead state process. 
     
     
       9. The plasm-generating system of  claim 5 , wherein the fixed stub tuner is a quarter wavelength fixed stub tuner. 
     
     
       10. The plasma-generating system of  claim 5 , wherein the fixed stub tuner is electrically shorted to prevent microwave radiation to the environment. 
     
     
       11. The plasma-generating system of  claim 5 , wherein the length of the stub is set prior to both the plasma ignition process and the stead state process by translating a length of a short segment of the tuner via a plunger assembly. 
     
     
       12. The plasma-generating system of  claim 5 , wherein the coupling antenna of the fixed stub tuner is inserted into a microwave cavity of the plasma applicator and positioned proximate to a plasma discharge tube of the plasma applicator within which the plasma is generated, the coupling antenna configured to couple power into the plasma. 
     
     
       13. The plasma-generating system of  claim 5 , wherein a segment of the fixed stub tuner is configured to become a portion of a coaxial cable transmission line connecting the fixed stub tuner to the microwave generator. 
     
     
       14. The plasma-generating system of  claim 1 , wherein an automatic impedance matching network is absent between the microwave generator and the plasma applicator. 
     
     
       15. The plasma-generating system of  claim 1 , wherein the coarse tuner is attached to an outer housing of the plasma applicator. 
     
     
       16. The plasma-generating system of  claim 1 , wherein, during the plasma ignition process, the microwave generator is configured to iteratively adjust the operating frequency without altering the at least one set physical parameter of the coarse tune until the ignition of the process gas is detected. 
     
     
       17. The plasma-generating system of  claim 16 , wherein the microwave generator iteratively adjusts the operating frequency by a predetermined step during each iteration within an operating frequency bandwidth of the microwave generator. 
     
     
       18. The plasma-generating system of  claim 1 , wherein, during the steady state process, the microwave generator is configured to iteratively adjust the operating frequency without altering the at least one set physical parameter of the coarse tuner to determine a maximum of the microwave power for maintaining the plasma in a steady state. 
     
     
       19. The plasma-generating system of  claim 18 , wherein the microwave generator iteratively tunes the operating frequency by a predetermined step during each iteration within an operating frequency bandwidth of the microwave generator. 
     
     
       20. The plasma-generating system of  claim 1 , further comprising an isolator located between the microwave generator and the coarse tuner to minimize reflected power from the plasma application to the microwave generator.